How should a worshiper pray if he doubts the number of rak'ahs he has prayed with the Imam and the number of rak'ahs remaining, and what is the correct procedure to complete the prayer in this situation?

The latecomer (masbuq) should build upon the minimum number of rak'ahs if he doubts the number of rak'ahs he prayed with the Imam and no particular number predominates in his mind. He should perform the prostration of forgetfulness (sujud al-sahw) before or after the salutation. There is no harm for him to build upon the prayer of someone who joined the prayer as a latecomer with him.